Field
The present disclosure generally relates to an information processing apparatus and an information processing method used for ophthalmic diagnosis and treatment.
Description of the Related Art
Ocular inspections are widely performed for the purpose of preemptive medical care for lifestyle-related diseases and high ranking diseases which cause a loss of eyesight. A scanning laser ophthalmoscope (SLO), an ophthalmic apparatus based on the principle of a confocal laser scanning microscope, performs raster scanning on the fundus of a subject eye by using laser (measurement light) to obtain a planar image with a high resolution and at high speed based on the light intensity of the return light. This apparatus detects, for example, only light that has passed through the inside of an opening (pinhole) and images only return light at a specific depth position, thus acquiring a planar image having a higher contrast than an image acquired by a common fundus camera. Hereinafter, an apparatus for capturing such a planar image is referred to as an “SLO apparatus”, and the captured planar image is referred to as an “SLO image.”
In recent years, an SLO apparatus has become capable of acquiring an SLO image of the retina with an improved transverse resolution by increasing the beam diameter of measurement light. However, with the increase in the beam diameter of measurement light, the signal to noise (S/N) ratio and decrease of the resolution of an acquired SLO image of the retina due to the aberration of a subject eye has become problematic.
To solve this problem, there has been developed an adaptive optics SLO apparatus (AO-SLO apparatus), an SLO apparatus having an adaptive optics for measuring the aberration of a subject eye in real time by using a wave front sensor and then correcting the aberration of measurement light and the return light occurring in the subject eye with a wave front correction device.
This adaptive optics SLO apparatus enables acquiring an SLO image having a high transverse resolution. Further, the adaptive optics SLO apparatus is capable of acquiring such an SLO image having a high transverse resolution as a moving image. Therefore, for example, to noninvasively observe the hemodynamics, the adaptive optics SLO apparatus is further capable of extracting the retinal blood vessels from each frame and measuring the moving speed of blood cells in the capillary vessels. When observing the visual cells, the adaptive optics SLO apparatus captures an SLO image by setting an in-focus position in the vicinity of the retina outer layers.
Furthermore, to evaluate the relation between the visual performance and the photoreceptor cells of the subject eye by using an SLO image, the adaptive optics SLO apparatus detects photoreceptor cells P illustrated in FIG. 6B and then measures the density distribution and the arrangement of the visual cells P. FIG. 6B illustrates an example of an SLO image with a high transverse resolution. The photoreceptor cells P, a low-luminance region Q corresponding to the capillary vessel position, and a high-luminance region W corresponding to the white corpuscle position can be observed from the SLO image illustrated in FIG. 6B. When observing the photoreceptor cells P, the adaptive optics SLO apparatus sets an in-focus position in the vicinity of the retina outer layer B5 illustrated in FIG. 6A and then captures an SLO image as illustrated in FIG. 6B. Meanwhile, retinal blood vessels and branched capillary vessels run in the retina inner layers B2 to B4 illustrated in FIG. 6A. When an in-focus position is set in the retina inner layers and an SLO image is captured by using the adaptive optics SLO apparatus, it becomes possible to directly observe, for example, the retinal blood vessel walls which are microstructures related to the retinal blood vessels.
However, in a confocal image of the retina inner layers in the SLO image, the observation of the blood vessel walls and the detection of wall boundaries may be difficult because of intense noise signals under the influence of reflected light from the nerve fiber layer. In recent years, there has been used a method for observing a nonconfocal image obtained by acquiring dispersion light by changing the diameter, the shape, and the position of a pinhole provided before an optical sensor (for example, refer to Non-Patent Document 1 (described below)). In a nonconfocal image in the SLO image, it is easy to observe an object having irregularities in the depth direction such as blood vessels because of a large depth of focus. Further, since reflected light direct from the nerve fiber layer is not easily received, noise can be reduced.
In addition, when observing the photoreceptor cells in the retina outer layers, conventionally in the confocal image, mainly the photoreceptor outer segment is captured. Whereas it has been known that in the nonconfocal image, an image of irregularities of the photoreceptor inner segment (for example, refer to Non-Patent Document 2 (described below)) is captured. A region of the visual cells where the photoreceptor outer segment is lost due to initial lesion, however, the photoreceptor inner segment exists is differently observed between the confocal image and the nonconfocal image. In the confocal image, the relevant region is observed as a black missing region (see FIG. 6G). In the nonconfocal image, the relevant region is observed as a region where high-luminance granular objects exist (see FIG. 6H).
Non-Patent Document 1 discusses a technique for acquiring the nonconfocal image of the retinal blood vessels by using an adaptive optics SLO apparatus. Further, Non-Patent Document 2 discusses a technique for simultaneously acquiring the confocal image and the nonconfocal image by using an adaptive optics SLO apparatus. Japanese Patent Application Laid-Open No. 2014-178474 discusses a technique used when capturing an image of a preparation that holds a sample by using a microscope. The technique calculates a provisional in-focus position of an object lens included in a first optical system based on an image acquired through a second optical system having a depth of field larger than the first optical system. Then, an in-focus position of the object lens based on the provisional in-focus position and an image acquired through the first optical system are searched for.